Do Now: What is the chemical formula of aluminum oxide?
Man, this is too much work! Is there an easier way????
Aim: How do we get the formula of a binary ionic compound?
Refer to the PERIODIC TABLE
1. To get the subscripts, just “criss-cross” the oxidation states and drop
the signs (+/-).
“criss-cross”
magnesium fluoride potassium oxide
MgF2 K2O
-Don’t write “1” for a subscript; the symbol of the element stands for “1”.
-All of these compounds end in –ide b/c they are binary = consist of
only 2 elements.
-The subscripts in a formula indicate the number of ions of each element
needed to form a neutral compound.
